Women taking the birth control pill have a slightly higher risk of cervical cancer, but that risk disappears a decade after they stop taking it, scientists say.
International researchers reported Friday in the British medical journal The Lancet that women who took the pill for at least five years had nearly double the cervical cancer risk of women who had never taken the pill.
But that risk is small and outweighed by the fact that the pill reduces the threat of other forms of cancer, The Lancet report said.
In developed countries, women up to the age of 50 who have never used oral contraceptives have a 3.8 in 1,000 risk of developing cervical cancer. That rises slightly to 4 in 1,000 for women who use the pill for at least five years, and 4.5 in 1,000 for those who use it for a decade.
In developing countries, taking oral contraceptives raises the risk of cervical cancer from 7.3 in 1,000 to 8.3 in 1,000.
"The bottom line is that this is a very small risk," said Dr. Debbie Saslow, director of breast and gynecological cancer at the American Cancer Society. Saslow was not linked to the study.
Cervical cancer cases typically affect women in their 30s — when many may be on the pill.
Previous research has linked the pill to cervical cancer, but the Lancet study appears to show for the first time that this connection is temporary. Ten years after women stop taking oral contraceptives, their risk for cervical cancer is virtually the same as that for women who never took them.
The research was led by Dr. Jane Green of Cancer Research UK's epidemiology unit at the University of Oxford.
Green and colleagues examined data from 24 studies worldwide, including 16,573 women with cervical cancer and 35,509 without it. The study was funded by the World Health Organization, the International Agency for Research on Cancer and Cancer Research UK.
Experts are not sure why oral contraceptives — which contain estrogen and progestagen — might increase the cervical cancer risk. The contraceptives also are thought to raise the chance of breast cancer, which may be triggered in part by hormone imbalances.
But those same hormones can protect against other cancers such as ovarian and womb. And unlike cervical and breast cancer, there is no way to screen for ovarian or womb cancer.
"The small increases in risk for cervical and breast cancers are outweighed by reduced risks for ovarian and womb cancer," Green said in a statement.
Doctors said that as long as women are routinely screened for cervical cancer, the increased odds that come with the birth control pill should not cause concern. If detected early, cervical cancer is potentially curable.
"Fear of cervical cancer should not be a reason to avoid use of oral contraception," wrote Peter Sasieni of Queen Mary University of London, in an accompanying commentary in The Lancet.